Transformer Models for Transient Studies Based on Field Measurements

A variety of models has been developed to represent transformers in switching surge studies. However, there is a paucity of data on the characteristics of large power transformers to provide parameters for utilization in the models. This paper describes a low power field method of saturating large transformers and plotting the instantaneous magnetization curve. Results on a 25 MVA unit allowed the accuracy of several equivalent circuits to be compared. Minor hysteresis loops were observed to obey simple relationships from which two magnetizing inductance models were developed